LOW FREQUENCY BANDWIDTH LASER

摘要

A narrow frequency bandwidth/high coherence laser light source is created by launching light from a laser diode (10) into a monomode optical fibre (12) containing a Bragg grating (16), made up of regions of fibre (14) of higher refractive index. The extent of the fibre from the laser up to, and including the grating (16) is retained within a temperature controlled cavity (20), preventing alterations in the pitch of the grating, or its separation from the laser due to thermal expansion. The grating is created by means of the exposure of the fibre to a periodic ultra violet pattern, which is in turn created by passing U.V. light through a phase grating. During manufacture, the output wavelength of the laser, and grating pitch and separation of the grating from the laser are matched, and the extent of the reflectivity of the grating (16) is then adjusted in dependence upon the coherence of light transmitted through the grating (16).